Provide a way to force stdout output in Gradle tests

libraries/tools/kotlin-gradle-plugin-integration-tests/src/test/kotlin/org/jetbrains/kotlin/gradle/BaseGradleIT.kt

@@ -73,7 +73,8 @@ abstract class BaseGradleIT {
             val daemonOptionSupported: Boolean = true,
             val incremental: Boolean? = null,
             val androidHome: File? = null,
-            val androidGradlePluginVersion: String? = null)
+            val androidGradlePluginVersion: String? = null,
+            val forceOutputToStdout: Boolean = false)
 
     open inner class Project(
             val projectName: String,
@@ -141,12 +142,15 @@ abstract class BaseGradleIT {
             setupWorkingDir()
         }
 
-        val result = runProcess(cmd, projectDir, env)
+        val result = runProcess(cmd, projectDir, env, options)
         try {
             CompiledProject(this, result.output, result.exitCode).check()
         }
         catch (t: Throwable) {
-            System.out.println(result.output)
+            // to prevent duplication of output
+            if (!options.forceOutputToStdout) {
+                System.out.println(result.output)
+            }
             throw t
         }
     }

libraries/tools/kotlin-gradle-plugin-integration-tests/src/test/kotlin/org/jetbrains/kotlin/gradle/util/gradleRunningUtils.kt

@@ -1,7 +1,7 @@
 package org.jetbrains.kotlin.gradle.util
 
+import org.jetbrains.kotlin.gradle.BaseGradleIT
 import java.io.File
-import java.io.StringWriter
 
 class ProcessRunResult(
         private val cmd: List<String>,
@@ -20,7 +20,12 @@ Executing process was ${if (isSuccessful) "successful" else "unsuccessful"}
 """
 }
 
-fun runProcess(cmd: List<String>, workingDir: File, environmentVariables: Map<String, String> = mapOf()): ProcessRunResult {
+fun runProcess(
+        cmd: List<String>,
+        workingDir: File,
+        environmentVariables: Map<String, String> = mapOf(),
+        options: BaseGradleIT.BuildOptions? = null
+): ProcessRunResult {
     val builder = ProcessBuilder(cmd)
     builder.environment().putAll(environmentVariables)
     builder.directory(workingDir)
@@ -29,11 +34,16 @@ fun runProcess(cmd: List<String>, workingDir: File, environmentVariables: Map<St
 
     val process = builder.start()
     // important to read inputStream, otherwise the process may hang on some systems
-    val sw = StringWriter()
-    process.inputStream!!.bufferedReader().copyTo(sw)
+    val sb = StringBuilder()
+    process.inputStream!!.bufferedReader().forEachLine {
+        if (options?.forceOutputToStdout ?: false) {
+            System.out.println(it)
+        }
+        sb.appendln(it)
+    }
     val exitCode = process.waitFor()
 
-    return ProcessRunResult(cmd, workingDir, exitCode, sw.toString())
+    return ProcessRunResult(cmd, workingDir, exitCode, sb.toString())
 }
 
 fun createGradleCommand(tailParameters: List<String>): List<String> {